The present invention relates to a surface mounting four terminal current sensing resistor of very low ohmic value and high stability.
Surface mounted current sensing resistors have been available for the electronic market for many years. Their construction comprises a flat plate made of a resistive alloy like the Cu—Mn—Ni alloy onto which are plated lands of high conductivity metal forming the four terminals. The voltage-sensing node is set in the resistive alloy.
When applied to ohmic values in the range of a few millohms or less, this construction introduces additional Joule losses due to the resistance between the point of connection of the current carrying wires and the a/m nodes. This leads to an additional temperature rise and results in drifts of the measurements.
The primary object of this invention is to provide an improved very low value surface mounted current sensor characterized by high stability when subjected to high ambient temperatures and to pulses of high power.
A further object of this invention is the provision of a resistor made of an alloy of high resistivity in order to increase its thermal capacity.
A still further object of this invention is the provision of a resistor in which the dimensions of the resistive plate are chosen in a way to minimize the length of the trimming cuts thus avoiding hot spots at points where the current makes a turn of 180 degrees.
A still further object of this invention is the provision of a resistor with terminals made of thick, high thermal conductivity material, which acts also as a heat sink during a power pulse.
A still further object of this invention is the provision of a resistor, which is constructed in a way to be capable of withstanding pulses of high power by choice of materials withstanding high temperatures and by reducing thermal resistance within the resistor.
A further object of this invention is the provision of a resistor which can be mass produced by stamping, laser trimming and coating by methods described in U.S. Pat. No. 5,604,477 and which can receive a high power rating when cemented to a metal base for soldering to a heat sink.
A still further object of this invention is the provision of a resistor that has terminals plated, for interconnection either by soldering or by welding.